Various graphitic materials are commonly employed as an active material for negative electrodes in lithium-ion batteries. In the process of manufacturing these electrodes, N-methyl pyrrolidone (NMP) has frequently been used as a solvent for the manufacture of electrodes for lithium-ion batteries. For example, the electrode graphitic materials have been generally dispersed in NMP containing a dissolved polyvinylidene fluoride (PVDF) binder. This slurry is coated on a metal foil current collector in a wet coating process; the coating is dried and roll-pressed to the required electrode density. Both the dispersion and wet coating process require a defined rheological behavior of the slurry (i.e. high viscosity at low shear rates for sedimentation stability and thixotropic behavior for proper mixing at high shear rates).
The recent introduction of the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals) in Europe and similar regulations in other parts of the world, however, has led to severe restrictions for the use of NMP. NMP is classified as a substance of very high concern and suspected to be a reproductive toxicant. Thus, in the field of electrodes, NMP or other organic solvents should be replaced by, for example, water, which consequently requires electrode materials that are suitable for the aqueous coating process.
The replacement of NMP or organic solvents, in turn, has led to another problem, caused by the hydrophobicity of known carbonaceous negative electrode materials. This hydrophobicity gives rise to an insufficient wetting of the carbon surface by water, thereby causing unstable dispersions. These properties lead to difficulties in the coating process, such as                i) agglomerates of undispersed carbonaceous particles that may create defects in the coating,        ii) enhanced sedimentation and binder segregation that create inhomogeneities in the coating and uneven electrode surfaces affecting the electrochemical performance of the electrode,        iii) high viscosity, especially at higher solid contents, which do not allow for proper mixing; and/or        iv) long processing time until the hydrophobic carbon material is homogeneously dispersed in the water-based slurry.        
In current processes in the industry, these problems have to be addressed by sophisticated and expensive dispersion techniques and the use of dispersants that stabilize the hydrophobic surface of the carbonaceous particles in water.
In addition, the hydrophobicity leads to a further problem in connection with the use of binders. Typically, in water-based electrode manufacturing processes, water-soluble, hydrophilic carboxymethyl cellulose (CMC) binders in combination with styrene-butadiene rubber (SBR) latex binders are employed. However, known hydrophobic carbonaceous materials are not fully compatible with these water soluble binders. In order to exhibit stronger and more resilient (against chemical and mechanical degradation) binding interactions with these binders, the surface of the carbonaceous particulate material should contain hydrophilic functional groups.
Achieving favorable binding interactions between the carbonaceous particulate material and binders will yield beneficial effects, for example on the mechanical integrity of the electrode during cycling as the carbonaceous active material expands and contracts during Li intercalation and de-intercalation. Said favorable interactions further allow minimizing the amount of binder present in the electrode, mitigating any isolating effects that the binder may exhibit on the electrical conductivity of the electrode, and maximizing the active material content in the electrode, i.e. the energy density.
Furthermore, said favorable interactions mitigate binder migration and skinning effects that could potentially occur during electrode drying, which would negatively affect the electrical conductivity and the mechanical integrity of the electrode. A favorable mechanical integrity and electrical conductivity of the electrode leads to a homogeneous current density distribution and thereby to a favorable retention of charge and discharge capacity, especially at elevated currents.
Hydrophobic carbonaceous surfaces are for example created by the coating of graphite particles by a carbon layer used to decrease the BET surface area, the interface area and the reactivity of the graphite negative electrode towards the electrolyte. Low surface area carbon coatings improve electrochemical parameters of the carbon particles by decreasing charge losses, improving cell safety and charge/discharge cycling stability. Furthermore, coating with carbon leads to carbonaceous active materials with favorable pressing behavior, allowing for the manufacturing of electrodes that are sufficiently dense (densities typically in the range of 1.5-1.8 g/cm3) upon pressing at typical process pressures of about 40 kN/cm2, while maintaining a favorable pore network between particles to allow for lithium diffusion between the electrolyte and the electrode. In contrast, electrodes fabricated based on uncoated graphitic materials frequently exhibit very high densities of >1.9 g/cm3, which causes unfavorable diffusion paths for the lithium ions in the electrode pores and therefore a lithium insertion rate restricted by the lithium ion diffusion in the electrode pores.
Although the need to produce hydrophilic carbonaceous particulate materials has grown over the years, only very few processes have been described to produce such hydrophilic carbonaceous particulate materials. Typical surface-coating processes resulting in hydrophobic surfaces are based on a coating of coal tar pitch on carbonaceous particles such as graphite in a dry- or wet-mixing process and a subsequent carbonization at elevated temperature in an inert gas atmosphere [Wan et al., Journal of Applied Electrochemistry, 2009, 39, 1081; Yoon et al. Journal of Power Sources, 2001, 94, 68]. Another known process described in the art includes the coating of pyrolytic carbon at the graphite surface achieved by treating the graphite particles in hydrocarbon vapors at elevated temperatures (chemical vapor deposition), typically referred to as CVD coating [Han et al., Electrochimica Acta, 2003, 48, 1073; Lopez-Honorato et al, Carbon 2009, 47,396; Liu et al, New Carbon Materials, 2008, 23, 30].
WO 2013/149807 describes surface-modification processes for synthetic graphitic particles obtainable by either an oxidative treatment or, alternatively, by chemical vapor deposition (CVD) coating, which provides graphite materials having improved surface properties. Although both processes are fundamentally different and produce distinct graphitic particles, both processes lead to graphite particles having advantageous properties over unmodified graphite per se.
Having regard to the prior art discussed above, it is therefore an object of the invention to provide surface-modified carbonaceous particulate materials characterized by a hydrophilic surface and exhibiting improved properties, as well as processes for making such materials having favorable physicochemical and electrochemical properties, particularly when used as a material for negative electrodes in lithium-ion batteries.